Apparatus for measuring the density of liquids



O. WEISS March 4, 1947.

APPARATUS FOR MEASURING THE DENSITY OF LIQUIDS Filed Jan. 20, 1944 2 Sheets-Sheet l f f x700/ "..f/ Y .,2/ :i

ATTGRN Y March 4,1947. Q. WEISS 2,416,808

APPARATUS FOR MEASURING THE DENSITY 0F LIQUIDS Filed Jan. 20, 1944 2 Sheets-Sheet 2 INVf; 5410K,

05u/AR wmss be 'WWW ATTORNEY- Patented Mar. 4, 1947 ZAlt APPARATUS FOR MEASURING THE DENSITY GF LIQUIDS @scar Veiss, Johannesburg, Transvaal, Union of South Africa Application January 20, 1944, Serial No. 518,944 In the Union of South Africa October 28, 1943 4 Claims.

invention render it well adapted for dealing with y non-homogeneous liquids.

A particular object of the invention is the continuous and automatic recording of the density measurement, or at least the indication of it at a distant station. In such eases it is practically a necessity that the recording or indicating mechanism shall be fixed in space; with the result that any variation of the height of the airliquid surface in which the hydrometer floats becomes a problem to be dealt with, since it introduces variations of the float height, with reference to fixed parts, additional to those due to changes of density of the liquid.

Cases in which the density measurement has necessarily to be taken while the liquid is in flow, are that in which the flow is due to the needs of an industrial operation to which the liquid is being subjected, and that in which the liquid is kept in flow in order to maintain in suspension constituents that tend to settle out. Ore pulp in circuit in a metallurgical plant is an instance Where both these conditions are present.

In the industrial operations mentioned, variation of rate of flow is to be expected; and such varia-tions involve variation of the height, With reference to xed parts, of the air-liquid surface at which the hydrometer floats.

The invention deals with this problem of variation of surface height by measuring the different immersion factors of two buoyant bodies floating in the same air-liquid surface of the liquid to be tested. The immersion factor means the magnitude of the rise or fall of a floating hydrometer consequent on a given change of density of the liquid. It is a function of the ratio of weight o-f the hydrometer to the horizontal cross sectional area of the hydrometer at the water line.

Considered from another aspect, the invention measures the height, with reference to fixed parts, of a hydrometer floating in said air-liquid surface, measures also the similar height of said surface and obtains the density of the liquid from the difference of said measurements.

More specically it is an object of the invention to transmit to the stationary measuring device only those movements of the buoyant bodies which they execute relatively to each other W- ing to a change of the density of the liquid and irrespective and independent of any common movement which the buoyant bodies might execute owing to a change of the level of the air-liquid surface.

Measurement of the density of liquid in now also raises a problem of another kind viz. that of presenting an air-liquid surface suitable for floating the hydrometer. The invention deals with this problem by flowing the liquid upwardly and causing it to overflow a horizontal rim, thereby providing a materially horizontal airliquid surface at which the hydrometer means is floated.

An example of apparatus according to the invention is illustrated in the accompanying drawings in which Figure I is a perspective view partly sectioned and partly diagrammatic, of a densimeter suitable for continuously recording the density of metallurgical pulp flowing from a classifier.

Figure II shows a modification of the recording part of the apparatus.

Figure III shows an alternative construction of the recording part of the apparatus.

The apparatus comprises a U tube lil, Il through which the pulp or other liquid to be tested is caused to flow continuously from a feeding launder l2 to a discharge launder I3 from which it is passed on for further treatment.

The pulp flowing up the upcast leg H of the U-tube overflows at the rim 0r lip I4 of the upper en d thereof and so provides the materially horizontal pulp surface l5. Said leg shapes the stream to a cross sectional form which does not vary with variation of rate of flow. The flow, being upward, is directly opposed to the settling tendency of the solid particles of the pulp; consequently, the rate of ow being made suihcient to keep said particles in suspension, there is nothing to prevent the stream from being of uniform density over its whole cross section. By forming the tube as a U, the downcast leg it adds to the length available for shaping the stream and ensuring its stream-line flow; whilst providing a liquid-propelling head that is uniform apart from the small changes due to variation of the rate of ow. It also reduces to a minimum the loss of head required to bring about the upward flow.

It is at the surface l5 that the floats it, il, i8 forming part of the apparatus are provided. The iioat marked i6 is essentially an ordinary hydrometer float characterised by a high immersion factor due to its weight being considerable relatively to its cross sectional area; so that small changes of density of the liquid are reflected as substantial changes of its immersion in the surface i5.

The other two oats il, i8, are functionally a single unit, structurally divided into two parts in order to be symmetrically positioned with respect to the axis i9 of the surface l5 since said surface is not quite level in the vertical cross section shown, although it is symmetrical with respect to said aXis.y Said two floats il, i8 are identically shaped and their immersion factor is low in oontrast to that of iloat it; that is to say they are of large horizontal cross section relatively to their weight, so that their depth of immersion is very small as compared with that of the hydrometer float; and, being very small, is very little varied by changes of density of the liquid.

Accordingly all three floats it, il, and iii are equally displaced vertically by whatever change occurs in the height of the surface i from time to time. A further component of the total verti cal motion of the floats is imposed by change of the density of the pulp; so that by subtracting total vertical displacement of l'i, it from simultaneous total vertical displacement oi ifi, the vertical displacement due to changes in the velocity oi flow is eliminated and the remaining displacement is a linear function of density. If the immersion of l?, i8 is but slight, its variation is negligibly small and the result of the subtraction ls a direct measure of the pulp density, like that given by the graduations of a simple free floating hydrometer.

The purpose of the rest of the apparatus to be described, is to measure said difference and to exhibit its value by means of stationary indicating or recording apparatus. Such apparatus includes a balance beam 2i! pivoted at 2l for movement in a vertical plane. The hydrometer float l5 is connected to one end of said beam through the medium of a light rod 23 attached to a hanger 2d pivoted to the beam at the horizontal axis 25. 25 is a second and similar balance beam the pivot axis 2l of which is vertically above the aXis 2l of beam Zil. The floats il, i8 are attached to beam 26 by light rods 2S, i@ and the hanger 3i). Si, 32 are dashpots associated severally with the beams to moderate their rate of tilting. Each beam with all its parts, but with the exception of the floats i5, l'l, i8, is somewhat precisely balanced by the mass 33 or 3d adjustable along it. The floats are made of sufficient size to provide the small amounts of power needed to operate the balance beams without themselves being materially displaced from their free floating positions. The constructional methods adopted in producing the apparatus are such as to minimize mass and friction.

As the result of this arrangement and provided the beams do not move far from the horizontal, change of level of' the surface l5 appears` as identical changes of angularity of both balance beams 2i), 23. Change of density on the other hand appears as change of the angle between the two beams and consequently as change in the vertical distance between two points, one on each beam, each point being at the same radial distance from the pivot axis 2l or 2l of its beam ard said points being vertically above one another.

Threek means are shown responsive to change of distance between two such points. In the Figure I arrangement such two points are represented, with suiicient accuracy so long as the beams remain materially horizontal, by two condenser plates 35, 35 mounted respectively on the 4, masses 33, 3ft which are in this case made of insulating material. Said plates 35, 35 are covered by insulating plates 38 to prevent their touching. A constant electrical potential derived from a source 39 and applied to condenser plate 36 induces a potential in plate 35 proportionate in magnitude to the distance separating the two plates. Said induced potential is ampliiied; and the amplified potential is used to control a recorder.

In the drawing il indicates a tube ampliier. The mains supply to said amplifier is shown at iii. One of the condenser plates, viz, is com nected by lead i2 to the unearthed mains terminal t3. The other plate 35 is connected by lead Q4 to the input terminal iii of the ampliiier. Those portions of leads i2 and which are close to one another are shown, as indicated by double lines, as being enclosed in earthed metal tubes so as to avoid any direct iniluence upon lead 54 of the input lead i2 which carries the full potential of 39. The cart-hed tubes are electrically insulated by any suitable means from the condenser plate 3S and 3'?. The portion of the mains voltage reaching i5 is made proportional to the capacity between the condenser plates, by keeping the input impedance oi the amplifier fit much lower than the impedance of the capacity of the condenser plates. The output iii oi the amplifier is connected to the coil o any suitable electric recorder #it and determines the position of a recording pen on a time chart 5! the vertical dimensions of which represent values of specific gravity of the pulp. Variation of the distance between the condenser plates 3.2i, it alters the magnitude of the induced potential and accordingly of the output oi ainplier t@ resulting in the pen @19 moving to a new position.

In the modification shown in Figure Il, one end of a flexible cord 5i is attached to an eye 5?. on one beam for instance beam. B3 and the cord is passed around the rim ci a pulley 5S mounted on the other beam. Said $2 and the ioint 5ft of the rim at which the cord passes on to the pulley 53 constitute the two points defined above as being vertically above one another and equally spaced from their respective beam axes 55, 56. Said cord 5i is also passed about a pulley 5T which is spaced a negligibly small distance from the axis 55 o beam iii?, .in the sense that displacement in space of said pulley 5l due to tilting of said beam does not signicantly alter the position in space oi the second end 53 of the cord 5l, which is led out from pulley 5l', close to and parallel with the axis 5G. Said cordend 58 is attached to the arm 55 of a pivoted member tti to move the latter against a light restoring spring 6l. Said member comprises an indicating or recording arm 52 working over a scale or chart 83.

An alternative mechanical arrangement is shown in Figure III. li is a frame positioned vertically and with its plane perpendicular to the plane in which the balance beams 2t, 26 move. Said frame provides guides E5 and tt on which a member 6l is free to slide horizontally with low frictional resistance due to the antifriction slippers 68, 69. Said member 5l provides a vertical guide 'l0 on which a carriage 'il is mounted for vertical movement, by means of the similar antifriction bearings l2.

Two equal links 'i3 are so pivoted to the carriage 'H that their ends 'ifi are free to separate and come together in the vertical direction. Said ends 'M are attached respectively to the balance S beams 29 and 26 by ball joints 15. The carriage 1I is connected by a rod 16 to the actuating 'arm 'Il of the pivoted member 18 which carries the indicating or recording arm 'I9 and is controlled by the spring 89.

Equal upward movements of the balance beams 20, 26 merely cause equal movement of the carriage 'll up or down the guide 19. Differential movement oi ae balance beams however causes alteration of the angle a between the links 13. This in turn causes horizontal displacement oi the member 6l, to or from the vertical plane in which the ends 'I4 of the links 13 work. The displacement is towards the balance if the balance beams separate, and away from the balance if the balance beams approach one another. This horizontal movement is transmitted by rod 'i6 to the actuating arm 'I7 of the indicating or recording device.

The movements of the pen 49 or the arm 62 may be calibrated against pulp flows of different densities; the values of which have been ascertained by other means. In an example of the apparatus constructed according to Figure I, the U-tube I9, H is ten inches in diameter and passes secondary classiiier overflow at the rate of 40 tons per hour. Normal variation of density is between 1.07 and 1.12; under which the hydrometer oat I6 rises or falls through a range of 11/2 inches reckoned from the surface l5. Variations in the rate of ow ci pulp are reflected as a range of 1 inch variation of the height of surface I5. By checking with systematically taken hand samples, the recorded density of the pulp is found to be correct within a margin of plus or minus 0.1 per cent.

I claim:

1. Hydrometer apparatus comprising means to present an air-liquid surface, a balance system comprising two buoyant bodies of diierent imf mersion factors to oat on said surface and a pair of similar balance beams to which said bodies are severally connected, said balance system adapted to displace said balance beams about equal angles on changes of the level of said air-liquid surface and about diiering angles on changes of the density of said liquid, a stationary measuring device and transmission means between said balance beams and said measuring device, said transmission means adapted to respond exclusively to the difference of said angular displacements but not to the angular displacements themselves.

2. The subject matter of claim 1 in which the bodies are substantially vertically below the beam ends to which they are connected, and the beam pivots are vertically one above the other, said transmission means including means to measure the vertical distance between similar points of the respective beams.

3. Apparatus for measuring the density of liquid, comprising means to dene an air-liquid surface of the liquid, two means displaced equally by variation of the height of the liquid and displaced unequally in the same direction by variation of the density of the liquid, two arms of equal length pivoted about separate axes so that they are capable of angular movement parallel with one another, said arms being connected respectively to the two means to be displaced therewith, a ilexible tensile member secured at one end to the end of one lever arm, means positioned respectively at the end of and near the pivot axis of the second arm for changing the direction of the flexible member, a movable measuring element, the flexible member being led around said direction changing means in succession and having its other end connected to said measuring element to move the latter, and resilient means for moving the measuring element in oppositicn to the pull of the iiexible tensile member.

4. Apparatus for measuring the density of liquid, comprising means to define an air-liquid surface of the liquid, two means displaced equally by variation of the height of the liquid and displaced unequally in the same direction by varia-v tion of the density of the liquid, two balance beams of equal functional length pivoted about separate axes so that they are capable of angular movement parallel with one another, said beams being connected respectively to the two means so as to be displaced therewith, two links enclosing an angle between them and each having one end pivoted respectively to each of said beams, and lying in a plane perpendicular to the plane of movement of the beams, a member movable in both dimensions of the plane of said links, the

,z-j, other ends of the links being connected to said member to combine the movements of both beams in said member, means so associated with the member as to derive therefrom only its one dimensional movement in the direction perpendicular to the plane of movement of said beams, which is due to change or" the angle between the links, and a movable measuring element actuated by such derived movement.

OSCAR WEISS.

REFERENCES CITED rEhe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 17,728 Burningham et al. July 15, 1930 1,691,084 Schwartz Nov. 13, 1928 1,701,404 Dennis Feb. 5, 1929 1,787,132 Van Orsdale Dec. 30, 1930 1,788,465 Lamar Jan. 13, 1931 1,838,845 Lanaux Dec. 29, 1931 2,294,455 Haultain Sept. 1, 1942 1,431,638 Dowling Oct. 10, 1922 1,526,850 Davis et al Feb. 17, 1925 1,071,167 McDonald Aug. 26, 1913 1,067,073 Steiger July 8, 1913 1,957,941 Coe May 8, 1934 2,211,748 Devenish Aug. 20, 1940 FOREIGN PATENTS Number Countr, Date 166,431 British July 21, 1921 446,069 British Apr. 23, 1936 64,514 German Sept. 19, 1892 630,435 German May 28, 1936 667,829 French June 25, 1929 690,716 French June 24, 1930 

